A batch-type vapor deposition apparatus that includes a susceptor having a plurality of recesses on an upper surface thereof and simultaneously processes a plurality of wafers, for instance, made of silicon has been typically known.
An epitaxial wafer manufactured by such a vapor deposition apparatus is used for a power device represented by IGBT (Insulated Gate Bipolar Transistor). In the epitaxial wafer used for the power device, an epitaxial film thickness is large and often reaches about 100 μm. With such a thick film thickness, although the wafers are respectively mounted in the recesses on the susceptor, a sticking phenomenon (hereinafter, referred to as “sticking”), in which an inner circumferential surface of each of the recesses and an outer circumferential surface of the corresponding wafer stick to each other due to deposits called “bridge” extending therebetween, easily occurs. When the sticking occurs, an epitaxial film at a sticking part needs to be peeled off in removing the wafers from the susceptor after the epitaxial film growth. At that time, since a considerable force is applied on a peripheral portion of each of the wafers, some of the wafers are often cracked to be occasionally broken.
Accordingly, various studies for restraining occurrence of the sticking have been made (see, for instance, Patent Literature 1: JP-A-2004-327761, Patent Literature 2: JP-A-2007-227838, and Patent Literature 3: JP-A-2008-187020).
In Patent Literature 1, a convex portion is provided on a bottom of the recess of the susceptor in a manner to project from a peripheral portion thereof. With this arrangement, even when the wafer is moved in a radial direction by centrifugal force in association with rotation of the susceptor, a tapered surface on a rear side of the peripheral portion of the wafer is brought into contact with the convex portion, thereby concentrically holding the wafer in the concave portion, so that the occurrence of the sticking is restrained.
Patent Literature 2 discloses that, when the wafer is freely dropped from a delivery robot into the concave portion, such free dropping of the wafer is disturbed by residual gas in the concave portion, so that the wafer is placed at a position deviated from a target position. In order to solve this problem, in Patent Literature 2, the susceptor and a rotary mechanism around a vertical axis of the susceptor is slightly inclined, so that the bottom of the recess is inclined. With this arrangement, an interval between the freely dropped wafer and the bottom of the recess is partially changed, thereby discharging the residual gas only in one direction to smoothly remove the residual gas, so that the wafer is restrained from being placed at a position deviated from the target position.
In Patent Literature 3, it is focused that an increase in a surface roughness of the bottom of the recess and a decrease in a contact area between the wafer and the bottom of the recess are important for effectively preventing the sticking between the rear side of the wafer and the bottom of the recess and that the sticking between the rear side of the wafer and the bottom of the recess occurs only on the peripheral portion of the wafer and does not occur on the center thereof. Based on these findings, Patent Literature 3 is arranged so that surface roughness on a peripheral area of the bottom of the recess is larger than surface roughness on the central area thereof.
However, in the arrangement of Patent Literature 1, since the rear side of the wafer and the inner circumferential surface of the recess are in contact, the sticking may possibly occur at this contact part.
In the arrangement of Patent Literature 2, since the rotary mechanism around the vertical axis of the susceptor is inclined, when the recess is moved in association with the rotation of the susceptor to be positioned lower in an inclined direction than a rotary axis, the inclined direction of the recess and the direction of centrifugal force are aligned to move the wafer to a lower side in the inclined direction. As a result, the wafer is brought into contact with the inner circumferential surface of the recess by the centrifugal force in association with the rotation of the susceptor, which may possibly cause the sticking.
Further, in the arrangement of Patent Literature 3, since no countermeasure against shifting of the wafer in the recess is taken, the wafer and the inner circumferential surface of the recess are brought into contact with each other, which may possibly cause the sticking.